The near-infrared polarization of the pre-planetary nebula Frosty Leo

Abstract

ABSTRACT We present a near-infrared imaging polarimetric study of the pre-planetary nebula: Frosty Leo. The observations were carried out in J, H, and K′ bands using the new polarimeter POLICAN mounted on the 2.1-m telescope of the Guillermo Haro Astrophysical Observatory, Sonora, Mexico. The most prominent result observed in the polarization maps is a large and well-defined dusty envelope (35 arcsec diameter in H band). The polarization position angles in the envelope are particularly well ordered and nearly parallel to the equator of the nebula (seen in J and H bands). The nebula presents a known bipolar outflow and the envelope completely wraps around it. Within the bipolar lobes, we find high polarization levels ranging from $60{{\ \rm per\ cent}}$ (J band) to $90{{\ \rm per\ cent}}$ (K′ band) and the polarization angles trace a centrosymmetric pattern. We found the remnants of superwind shells at the edges of the bipolar lobes and the duration of this phase is around 600 yr. The origin of polarization features in the nebula is most likely due to a combination of single and multiple scattering. Our results clearly demonstrate new structures that provide new hints on the evolution of Frosty Leo from its previous asymptotic giant branch phase.